In a large mixing bowl, combine chicken with juice, chilies, rotel, diced onion, water and cream of mushroom soup. In a separate baking dish, pour a layer of wet mixture, then layer it with cheese, then a single layer of tortillas. Keep re-layering until you get to the top of the dish. Top with remaining shredded cheese. Bake at 350° until cheese is melted, about 25-30 minutes.